In recent years, there has been increasing emphasis on shielding computer information display devices, such as cathode ray tube (CRT) screens both to prevent certain types of ambient electromagnetic interference or radiation from penetrating the screen and to prevent certain types of electromagnetic interference or radiation from exiting the screen while permitting information on the screen to be readily viewed by a computer operator. Generally, such shields, or filters, have taken the form of conductive metal meshes laminated between glass and/or plastic panels disposed across the front of the screen and appropriately grounded to the cabinet in which the screen is mounted.
An improved CRT screen filter of this general nature is disclosed in U.S. Pat. No. 4,514,585 entitled "Filter and Method of Manufacturing" issued to one of the applicants herein. In the patented filter, an impregnated conductive metal mesh is bonded to and forms a surface of a plastic panel which is disposed across the front of the cathode ray tube and grounded peripherally to the cabinet in which the tube is mounted. The filter absorbs various types of radiation generated by the cathode ray tube and prevents various types of radiation from penetrating the cathode ray tube.
There are available computer terminals having so-called touch panels extending across the front of the computer information display screen for displaying separate regions, or menu blocks, of printed information, or indicia, within an area thereof. The touch panels are associated with various means for producing a computer-responsive signal depending upon which of the separate regions is touched by an object, such as a pointer, finger or the like. The signal operates in conjunction with conventional computer circuitry to perform various well-known computer related input functions.
Various means are utilized to determine which information block is touched. One such means includes a series of light beams which intersect in a grid-like pattern in front of the screen in registry with the various information blocks. The aforementioned computer-responsive signal is produced when the intersecting light beams are interrupted, such as when the computer operator's finger is positioned on one of the information blocks. The light beams are generally provided by light emitters and are received by light detectors both of which are located in front of the screen and are arranged in spaced relation to provide the grid-like pattern of parallel intersecting beams of light, as well known in the art.
The aforedescribed type of computer terminal touch panels have presented problems when it comes to radiation and interference shielding. For instance, the light emitters and detectors are located laterally of the screen and so are not shielded by conventional filters as described above. Moreover, the emitter and detector pairs are known to be highly sensitive to stray radiation, generated internally of the screen and externally thereof, but it is difficult adequately to shield the same because of the need to project light beams over a range of wavelengths of sufficient intensity as to provide satisfactory location sensing performance under a wide range of ambient lighting conditions. Accordingly, there is not currently available commercially satisfactory means for shielding a computer terminal having such touch panels.